The use of filled polyester resins as sheet molding compounds (SMC) and/or as bulk molding compounds (BMC) is well established. In general, it is desirable for such compositions to contain as much filler as possible in order to increase the stiffness as well as to improve the surface quality of the molded products. Unfortunately, the addition of large proportions of filler increases the viscosity of molding compositions thereby leading to processing difficulties, as well as, to difficulties in wetting out reinforcing fibers which may be present and in allowing entrapped air to be released.
In order to overcome the difficulties associated with such increase in viscosity, it has been proposed to add certain viscosity reducing agents to the moldable filled resin composition. In large part, the necessity of adding such an agent stems from the susceptibility of the polyester resins, typically employed, to commence cross-linking upon exposure to heat such that the mere heating of the mixture to lower its viscosity is precluded.
One commercially available additive which has been promoted as a viscosity reducing agent for such compositions is a polymeric material available from Byk-Chemie G.m.b.H. Thus, in Modern Plastics International, October 1986, at page 112, this material is described as being effective for the wetting and dispersion of mineral fillers in hot-curing glass fiber-reinforced unsaturated polyester resin to provide a reduction in impregnation viscosity.
Canadian Patent Application 2,022,957, to Haubennestel et al., discloses that certain phosphoric acid esters which are the reaction product of phosphoric acid with an oxyalkylated monoalcohol containing carboxylic acid ester groups and/or urethane groups can be similarly employed to lower the viscosity of SMC and/or BMC compositions.
While such materials have been found to provide some efficacy in reducing the viscosity of filled moldable polyester compositions, it would nevertheless be desirable to have additives which would yield filled compositions possessing at even lower viscosities.
The present invention provides a moldable filled composition which exhibits an unexpectedly low viscosity and which yields articles exhibiting desirable strength and surface properties.
In one aspect, the present invention is directed to a moldable composition comprising:
(A) a liquid polyester resin; PA1 (B) an inert filler; and PA1 (C) a compound of the formula: ##STR1## wherein: R is C.sub.4 -C.sub.18 alkyl, C.sub.4 -C.sub.18 alkenyl or C.sub.4 -C.sub.18 alkynyl; and PA1 n is 1 or 2. PA1 n is 1 or 2; in a solids or solid-liquid mixing device until a uniform mixture is obtained.
In another aspect, this invention is directed to a process for producing a moldable composition comprising blending (A) a liquid polyester resin; (B) an inert filler; and (C) a compound of the formula ##STR2## wherein: R is C.sub.4 -C.sub.18 alkyl, C.sub.4 -C.sub.18 alkenyl or C.sub.4 -C.sub.18 alkynyl; and